Derivatives and Risk Management Activities (Details 3) CAD in Millions, $ in Millions	Sep. 30, 2015 CAD CAD / $	Sep. 30, 2015 USD ($) CAD / $
Forward exchange contracts that exchange CAD for USD at the rate USD 1.00 to CAD 1.33 maturing in 2015
Currency Exchange Rate Risk Hedging:
Notional amount of derivatives	CAD 202	$ 152
Average exchange rate	1.33	1.33
Forward exchange contracts that exchange CAD for USD at the rate USD 1.00 to CAD 1.33 maturing in 2016
Currency Exchange Rate Risk Hedging:
Notional amount of derivatives	CAD 76	$ 57
Average exchange rate	1.33	1.33
Forward exchange contracts that exchange CAD for USD
Currency Exchange Rate Risk Hedging:
Notional amount of derivatives	CAD 278	$ 209
Forward exchange contracts that exchange USD for CAD at the rate USD 1.00 to CAD 1.28 maturing in 2015
Currency Exchange Rate Risk Hedging:
Notional amount of derivatives	CAD 222	$ 173
Average exchange rate	1.28	1.28
Forward exchange contracts that exchange USD for CAD at the rate USD 1.00 to CAD 1.28 maturing in 2016
Currency Exchange Rate Risk Hedging:
Notional amount of derivatives	CAD 73	$ 57
Average exchange rate	1.28	1.28
Forward exchange contracts that exchange USD for CAD
Currency Exchange Rate Risk Hedging:
Notional amount of derivatives	CAD 295	$ 230